Conventionally, a variety of compositions of dielectric ceramic materials have been investigated in order to adapt the ceramic materials to use in a high-frequency region such as the microwave region or the milliwave region, where dielectric characteristics such as a large relative dielectric constant, a small dielectric loss, and a small absolute value of temperature coefficient of resonance frequency are required. In relation to such dielectric ceramic materials, Japanese Patent Publication (kokoku) Nos. 2-53884 and 4-321 and other publications disclose dielectric ceramic materials having a BaNbO3 component. The Ba(Zn, Nb) dielectric materials disclosed in the above publications exhibit excellent characteristics; i.e., a high unloaded quality coefficient and a small temperature coefficient of resonance frequency.
However, the aforementioned Ba(Zn, Nb) dielectric materials do not necessarily exhibit a satisfactory percent maintenance of unloaded quality coefficient as expressed by percentage of unloaded quality coefficient measured at high temperature (approximately 125° C.) with respect to that measured at room temperature (approximately 25° C.). Therefore, when these dielectric ceramic materials are used in dielectric resonators and other apparatus, dielectric loss at high frequency problematically increases. In order to overcome this problem, researchers have pursued development of dielectric ceramic materials which exhibit improved dielectric characteristics and a small temperature dependency on resonance frequency and which maintain a high percent maintenance of Q value as expressed as a percentage of Q value measured at high temperature with respect to that measured at room temperature.